A photo-electric rectifier can be used as a switch or modulator in high-voltage systems. A photo-electric rectifier provides two electrodes, a photo-cathode and an anode, separated by a distance in a sealed vacuum tube. A photo-cathode is a negatively charged electrode that emits electrons when illuminated by a light source due to the photoelectric effect, wherein energy from photons striking the surface of the photo-cathode is acquired by electrons within the material of the photo-cathode, causing the electrons to be ejected. When the photo-cathode is illuminated, electrons are emitted, flowing through the interior of the vacuum tube to the positively charged anode, creating a flow of current between the two electrodes. When the illumination is switched off, no electrons are emitted, and the flow of current between the electrodes stops.
If high currents are generated in photo-electric rectifiers, this can cause problems as the system operates over time. Using high-voltage in a photo-electric rectifier can create impurities or contaminants. For example, high-voltage electrons bombarding the surface of the anode can cause the creation of ionized atoms in the vacuum tube. If the ionization of the atoms is caused by electrons being knocked off of the atoms, the atoms will become positive and will be attracted to the photo-cathode, which leads to the deposit of contaminants on the photo-cathode.
Reducing the voltage required within the photo-electric rectifier can reduce the creation of contaminants, but also robs the electrons that are ejected from the photo-cathode of energy, which suppresses their ability to travel to the anode to generate current. In other words, reducing the voltage required within the photo-electric rectifier can slow the rate that electrons clear away from the surface and can suppresses the fraction of electrons that will travel to the anode to become current. Using a traditional control grid with a positive voltage relative to the photo-cathode, such as those used historically in vacuum tubes, can help accelerate electrons toward the anode, but the relatively positive voltage of a typical control grid can also draw in and collect some percentage of those electrons, preventing them from completing the circuit to the anode, causing a drop in efficiency.
There exists a need for an efficient photo-electric rectifier which can operate at a lower voltage to reduce contamination while providing efficient, reliable operation in high-power systems.
It should be noted that the figures are not drawn to scale and that elements of similar structures or functions are generally represented by like reference numerals for illustrative purposes throughout the figures. It also should be noted that the figures are only intended to facilitate the description of the preferred embodiments. The figures do not illustrate every aspect of the described embodiments and do not limit the scope of the present disclosure.